1. Field of the Invention
The present invention is related to a device for a set of radio communication equipment to reduce electromagnetic energy absorbency of a human body, and especially to such a device particularly suiting the equipment of a PDA, a mobile phone, a Blue Tooth etc. that can reduce electromagnetic energy absorbency of a human body.
2. Description of the Prior Art
The fast growing of the market mobile phones indicates that the mobile communication equipment has high developing potentiality. Signals from a set of radio communication equipment such as a mobile phone are transmitted mainly with specific working frequencies (for example: 900 MHZ and 1800 MHZ); however, it is studied and showed that the signal transmission with such frequencies, especially those for mobile phones often being pressed against the area near a human brain for a long time, is probable to hurt the human body. And thereby, most countries and districts establish related stipulations on safe limiting values for such communication equipment.
Taking the FCC (Federal Communication Committee of the U.S.A.) as an example, the standard safe limiting values for the specific absorption rate (SAR) of electromagnetic energy of human bodies for a mobile phone are stipulated to be under 1.6 W/kg (1.6 mW/g), i.e., the amount of radiation of electromagnetic waves born by human shall be under 1.6 watts per kg (weight of a person). In Europe, the specification (CE) of safe limiting values is 2.0 mW/g. In view that in the modern related study of medical science, when heat energy converted from electromagnetic waves is absorbed by the brain tissue of a person and accumulated in the human body to make the internal temperature of the person increased to 4.5° C. for 30 minutes, it is reported that this may hurt the nerve tissues of the human body. In some countries, the requirement on safe limiting values for the specific absorption rate (SAR) is even severer.
The mobile phones now available are hard to get the above stated safe limiting values for SAR in their stages of study and development. Taking the test on mobile phones as an example, information of the test includes a chart of standing wave voltage ratios (VSWR) (FIG. 1), a table showing the values of different types of electromagnetic radiation fields (FIG. 2), charts showing effective radiated powers (EIRP) (FIGS. 3, 4) and a chart of sensitivity for receiving (FIG. 5).
As shown in FIG. 1, the (SWR) standing wave ratio at a lower frequency 880 MHz is 1.418, and 2.251 at 960 MHz; the (SWR) at a higher frequency 1710 MHz is 2.042, and 1.302 at 1880 MHz. And when it is tested under the channel 975, the effective radiated power (EIRP) is 32.08 dBM (FIG. 3), the average value of sensitivity for receiving is −104.68 (FIG. 5); but the SAR will be high up to 2.27 (mW/g), i.e., the safe limiting values of American specification and European specification are both lower than this value.